The key feasibility issue of slow recruitment is perhaps unsurprising, as issues with recruitment are common in RCTs.146A HTA monograph exploring this issue that examined 114 funded trials found that
only 31% successfully recruited to target and 45% achieved less than 80% of the original sample size.147
The authors also noted that it is more to difficult to recruit to target in non-drug trials. Additionally, it is likely that the rather complicated inclusion criteria, in particular the requirement of written verification of weight loss, compounded the issues we experienced with recruitment. Most of the 1284 people who expressed an interest in taking part in the trial were unable to provide written verification. We devoted a significant amount of resource to identifying potential participants with 5% weight loss from primary care and EOR, with limited success relative to effort (although primary care did provide 39% of recruits). This was primarily because records kept by GPs and EOR practitioners were not sufficient for our verification requirements. GPs often record weight but lack systematic monitoring, with the result that a 5% loss within a 12-month period is often not recorded in an easily searchable manner. Therefore, when written verification of weight loss is an entry requirement, recruitment routes linked to current or recent weight loss programmes (slimming clubs or concurrent weight loss trials) are likely to be most effective, although this may limit generalisability. In addition, delays in obtaining treatment and service support costs
(particularly in England), as well as governance delays, were related to our recruitment problems. Although the landscape has changed considerably since this trial, consideration should still be given to these issues as well as to obtaining infrastructure support and how this might vary between the devolved nations. Our reduced sample size and thus reduced power means that we are able to draw only limited conclusions about the impact of the intervention on BMI. This sample size is, however, considerably larger than many trials of WLM interventions.148–152In a systematic review of WLM following at least 1 month of intervention and then
1 year of no intervention, the sample sizes of the 12 included studies152(with 22 intervention groups)153–169
ranged from 44170to 241,171–173with only three studies having a larger sample size than the present study.
There are no studies of MI for WLM; however, in a review of studies using MI as an intervention for weight loss, only one-third of the 12 included studies had a larger sample size than the current study and the range was 22–599.64
Our retention rate for the trial is excellent and compares favourably with other trials of complex
behavioural interventions for weight loss or WLM, in which dropout rates can be high even at 1 year. A systematic review of long-term weight loss interventions found an average dropout of 29% at 1 year.25In
the MI review for weight loss,64two-thirds of included studies had a higher dropout than the current study
with a range of 8–35%; only one study had a longer follow-up than this study (18 months).53
With regard to the elements considered in the process evaluation, the intervention was delivered with good fidelity. There was evidence that practitioners covered the topics required by the WILMA study. The participants appeared to receive the intervention as intended because understanding of the purpose and methods of the counselling sessions was demonstrated. However, a couple of men had unfulfilled expectations of the sessions, anticipating a much more directive approach. In terms of adherence to the intervention, we had excellent adherence to the key face-to-face MI, at 87% overall. This compares favourably with adherence in other counselling-type interventions.53,59,174However, we did have an issue
with the group-based aspect of the intervention. Delivery of local group sessions on a rolling basis did not appear to be feasible, although the low recruitment rates had an impact on the ability to run these as planned. Other, less resource-intensive and less logistically challenging, approaches to providing social support that do not depend on a minimum recruitment rate should be considered in the design of any future trial. Telephone MI sessions were also not as successful as the face-to-face MI. There were a number of reasons for this, some of which could be addressed in future studies, including more training for delivering MI over the telephone, better reimbursement for MIPs to account for time taken in arranging these sessions, longer sessions and possibly sessions closer together, particularly for those in the less intensive arm. However, it was difficult to gauge the adherence rate because of poor return of paperwork. It is likely that more of these were completed than we have records for and participants in many cases found this contact useful. Evidence also indicates the importance of ongoing contact for WLM.38,175,176
For a feasibility study, both the qualitative and quantitative results look encouraging. As expected, there are few statistically significant results owing to the analyses being underpowered; however, there are promising mean differences and CIs on important outcomes. The intensive arm has a consistently larger treatment effect and generally in the direction of benefit, representing a clear signal that the intensive treatment potentially leads to improvements on a wide range of health-related outcomes. This leads us to suggest that any future trial should consider comparing only the intensive intervention with a control. Although weight loss in neither treatment arm was statistically significantly different to that in the control group, the odds of maintaining weight loss was 43% higher in the intensive arm than in the control group. According to CACE analyses, the average weight loss was 3.69 kg lower in the intensive arm relative to the control group. In the case of BMI, average BMI was 1.23 kg/m2lower in the intensive arm relative to the control group. This compares well with other trials, and this
degree of difference is likely to be clinically significant in this group of individuals, many of whom are probably at increased risk of cardiovascular disease. Several studies indicate that loss of 2–5 kg weight can lead to reductions in cardiovascular risk factors.11–14,177In a trial of MI delivered in five sessions in primary care, the mean
difference in BMI between the intervention and control groups was 0.36 kg/m2at 12 months (from end of
intervention) and 0.1 kg/m2at 6 months.178A recent systematic review of trials of behavioural interventions
(focusing on diet and physical activity) to help individuals maintain weight loss found an average weight difference of–1.56 kg in weight regain relative to controls at the 12-month follow-up.35If the findings in this
study were true differences, then this compares favourably with other trials. The Barteet al.152systematic review
of 12 studies found that the percentage of initial weight loss that was maintained after 1 year’s unsupervised follow-up ranged from 25% to 88% and the average was 54%. Four of these studies had an intervention period of 3 months or less, so were similar in length of follow-up to this study. This percentage maintenance has also been found in other systematic reviews20,149that have reported 50% maintenance at 1 year
With regard to the other secondary outcomes, there are few indications of an effect from the intervention, with the exception of the DINE fat and healthy eating scores and the number of days of binge eating. However, there are issues with the sensitivity of the measures to detect an effect, and measuring physical activity and diet accurately are particularly problematic.179,180
With regards to the theory testing and the mediation analyses, we are limited in what conclusions can be drawn from the analyses because they are underpowered. There does appear to be a relationship between a number of the mediators and outcomes, but we cannot say whether or not changes in these are
influenced by the intervention. In terms of studies using mediation analyses to look at the impact of MI, the evidence base is limited; however, there is mixed evidence of the impact of MI on self-efficacy.181–184
An impact of MI on self-monitoring was found in one study53while another that explored the link between
MI and motivation found that MI is related to increased autonomous motivation.183One study found that
an intervention using the core principles of MI led to improved planning as it generated more detailed action plans and longer duration of physical activity than the control.99One other study has noted the
importance of some of these mediators in WLM, including self-efficacy and intrinsic motivation.185
A recent systematic review looking at mechanisms of MI within health behaviours found that MI‘spirit’ and motivation were the most promising mechanisms of MI but concluded that there is a dearth of research exploring this issue, and more studies need to be completed.184
Another potential concern with the assessment of mediators is that the measurement tools we used may not have been sufficiently sensitive to detect a change. In addition, the timing of the measurement of the mediators could be important. If assessment does not occur at the critical time, then this could affect our ability to detect the impact of the intervention on these mediators and, thus, on outcome. We had originally planned a 6-month time point for assessment of mediators as we estimated this would be after all the face-to-face sessions would have been delivered and, therefore, participants would have had a full dose of intervention to influence these mediators. In the majority of cases this did happen, and 39 out of 54 participants in the intensive arm received five or six sessions of MI before their 6-month assessment. There is some support in the qualitative data for the theoretical underpinning of the intervention and thus the different elements of the logic model. Ongoing motivation was seen as central; however, other aspects, such as self-monitoring, self-efficacy, habit formation and social support, were all seen as important by participants. Ongoing motivation was strongly influenced positively and negatively by the support of others including family, friends, peers and professionals. Participants reflected on the MIPs’skills in MI of providing an empathic, non-judgemental environment in which they allowed individuals to control and direct their own plans for weight management. Professional support that was caring, objective and non-judgemental and provided psychological support was thought to be important. A good professional relationship helped with motivation because participants wanted to please their practitioner; it also provided the checking in or accountability elements that participants found useful.
Social support was discussed in detail by participants and was seen as key for WLM. Peer support was considered important because it provides accessible, regular opportunities for support, reduces isolation and provides opportunities for reinforcement, encouragement, feedback, role-modelling, instrumental support and comparison as well as learning from each other. Peer support is distinct from other support because of the shared experience, and it also provides opportunities to improve self-efficacy, which is integral to the psychological theories underpinning the intervention. Support from family and friends was also deemed important, particularly if these individuals were committed to maintaining a healthy lifestyle. If they were not, then often this led to temptation; for example, some family and friends deliberately tempted participants or, less directly, had a negative influence by bringing unhealthy foods into the house. Positive reinforcement was a crucial aspect of support and could come from direct reinforcement from peers or family. It also appeared to work independently to facilitate self-efficacy and maintain motivation, particularly the reinforcement acquired through continued weight loss or maintenance. Improvements in health also acted as a positive reinforcer.
Control was seen as important, and participants indicated that feelings of control were reinforcing and were important in relation to motivation. Conversely, loss of control could lead to bingeing and thus demotivation and feelings of failure; however, if the diet was too rigid and participants felt deprived, then failure was more likely. Participants suggested that control could be retained by taking a more flexible approach to their diet. Self-monitoring was seen as important to both weight loss and maintenance, in the form of regular weighing. Self-monitoring was described as helping people to feel in control. This was something that the majority of participants were carrying out prior to entering the study and was recognised by many as an important tool. The importance of control and not feeling deprived has been noted in other research.185,186
Routine and habit formation were described as important to longer-term maintenance of healthy behaviours, and the development of‘good habits’in relation to WLM was also part of the theory
underlying the WILMA trial intervention. Those who failed to develop healthy lifestyle habits continued to struggle with their weight management. There is evidence from the psychological literature about the importance of developing healthy habits, which are not effortful to maintain, and enhance maintenance of behaviour changes.187–189
The analyses also revealed some of the potential barriers faced by weight loss maintainers, including environmental and cultural barriers and the important role that food has within our society. The issues identified by participants make maintaining weight loss particularly challenging as so much of our lives revolve around food. There are inherent tensions in dealing with food, which is simultaneously a source of pleasure but is also at the heart of participants’struggles. It is not a behaviour that we can stop doing: we need to eat to live. Our environment presents a number of challenges, including the ready availability of high-fat unhealthy food relative to healthier options, which can make weight management difficult. Other people can help or hinder weight management through various direct and more subtle routes, as noted earlier.
There are few qualitative studies exploring WLM; however, those that have been completed have described many similar findings to the present study. Studies have indicated the importance of realistic goal-setting, use of routines, self-monitoring, avoiding deprivation and effective coping skills.186,190Another
study emphasised the importance of support during maintenance, problem-solving skills and motivation.191
Evidence from the qualitative literature on MI indicates that participants found monitoring to be useful when losing weight. They felt that being accountable to someone was helpful, especially when they struggled with self-monitoring, and they also mentioned increased motivation to change and an increased feeling of personal control.192A Swedish study193found that WLM was seen as a‘tightrope walk’and the
strategies that participants found useful in this regard were finding things to enjoy about WLM, such as nice foods and focusing on well-being rather than body weight; routine was seen as important, as was the support of significant others. Participants described the importance of being in control, and this included using self-monitoring.193In another study, the respondents described the presence of saboteurs as well as
the lack of positive reinforcement during the maintenance stage as a particular challenge.194
Although the cost-effectiveness results suggest that the interventions may not be cost-effective, we must again bear in mind that this feasibility study had a reduced sample size and was therefore underpowered to fully explore these issues. Moreover, the trial is about WLM, and a much longer follow-up period is needed to establish whether or not weight loss is maintained in the long term and thus whether or not the intervention is cost-effective at meeting its intended aim.
The main cost-effectiveness study focused on QALY gains based on EQ-5D scores. Although there is evidence to suggest that higher BMI is associated with lower EQ-5D scores,195obesity is largely considered a health
problem because of its association with raised risk factors for conditions including type 2 diabetes mellitus and cardiovascular disease. Therefore, success in terms of reduced BMI ought to produce long-term health gains in terms of reductions in the incidence and severity of these conditions and consequent reductions in health service treatment costs. An original aim of the WILMA study was therefore to estimate lifetime costs and
QALYs via economic modelling using trial-based data on BMI, EQ-5D and costs. This was dropped when the WILMA trial became a feasibility study.
The overall benefits of the interventions are nevertheless likely to be observed over a far longer time period, while the intervention costs are more short term and weighted to the early stages. The short-term nature of this analysis is therefore likely to be a lower bound for the potential cost-effectiveness of these interventions. Few trials of WLM or long-term weight loss have looked at cost-effectiveness. A HTA monograph suggests that there is some evidence that weight loss management interventions may be cost-effective; however, the authors suggest caution owing to methodological limitations of the two included studies.196